By Derek Daily, General Manager, Senju Comtek Corp., Campbell, CA Wave soldering processes generate a large quantity of dross with each and every PCB run through the line. With the introduction of lead-free applications, the amount of solder discarded has increased dramatically. Running a less complex solder fountain with the standard SAC305 alloy over a typical 8-hour work day may generate as much as 8 to 10 percent dross or more — 1 to 2kg per every 10 to 15kg in the bath. Dross generation increases significantly when used in higher bath temperatures — sometimes necessary for high-density, high-thermal mass type PCB builds.

Large Amounts of Dross GeneratedWith many lines running multiple shifts, the amount of dross accumulated becomes dramatic. Using a rather conservative 8 percent loss on a 500kg pot, an amount smaller than typical for a full scale wave system, 40kg of dross could easily be created per day in a production environment. Multiply this amount by the number of lines you have in operation and your financial officers will begin to see red ink. This increase in solder loss, when combined with the escalation of much higher raw materials market prices for tin and silver (approaching $40 to 45 per kg for SAC305) make any solder dross recovery program critical to cutting operational costs.

Because of this, it has become standard operating procedure for many assemblers to resell these scraps externally in an effort to recover at least some kind of minimum value back from the waste metals. Using an external program requires dross packaging and inventory, often necessitates complex contractual obligations with the original solder supplier and still returns relatively little value because of the transportation and processing costs for refining the materials.

Senju Metal Industry Co., Ltd. (SMIC) of Japan has been a manufacturer of soldering materials and related equipment for more than 75 years, and has developed a simple, efficient, and cost-effective method to internalize the recovery operation.

Using a patented process, the SMIC SDS2-5N Solder Recycle System is a semi-automated tool designed to reclaim the base solder alloy from the solder dross. It is designed to be operated at very low cost, does not require continuous operation when not in use, and has a complete cycle time of less than half an hour, from dross to a final refined alloy product.

Separating Useful Solder MaterialsAn operator would first remove dross from the bath and place it into the tool. Specially formulated sesame seed (E-Sesame) is mixed with the dross inside the system. Then, after heating and agitation inside the proprietary mixing chamber, a small amount of oil from the E-Sesame naturally acts to separate oxides from dross. The recovered solder alloy is then cast in a simple mold to make ingots that can be used in the plant's normal production line. The sesame oil and husks are removed in the oxide cleansing process.

Recycle recovery rates may reach as high as 90 percent, but a minimum of 70 percent recovery is typical. Recovery rates may vary depending on the condition of the dross and the amount of E-Sesame used. If E-Sesame is not available, you may also operate the Solder Recycle System, but at a reduced recycling recovery rate.

The SDS2-5N is compact, easy to use and one of the lowest cost recycling systems in the industry. ROI can reasonably be expected within a few months, rather than over the years of depreciation that is more typical with much larger capital equipment purchases. Customers now utilizing the tool usually have multiple systems, with dedicated tools for each line.

Whether you are manufacturing in a high volume, low-mix or very diverse product environment, dross will be generated. Basic SDS equipment allows refining of five kg batches per cycle. More advanced systems may be available on special order. The tool may be used to collect dross from SnPb or Pb-free alloy compositions. No special training is needed. Installation is also simple, just plug in the power and connect exhaust ducts.

SMIC has dozens of field service offices throughout the world, with multiple offices here in the Americas to support any technical questions. In addition to the field service engineers, several process engineers are available near our US solder production facilities.